"I don't want to say 'reboot' because then people will think we're doing a Spider-Man and starting from the beginning. We're not.

"We're taking the story that you've seen - the story we've told in three movies already - and we're taking it in a new direction. But we're leaving those three as the history. It all still counts... We're moving on to something different."

Bay also hinted that the film may partially be set in space.

"That feels like the way to go, doesn't it?" he said. "I want to go a little off [the planet] but I don't want to go too sci-fi. I still want to keep it grounded."

The director has already said that the fourth Transformers film will be his last.